Devices of the above-mentioned type are known and essentially comprise a control member adapted to assume four different positions along its first axis, each of which corresponds to the selection of a gear, and to assume three different angular positions contained in planes at right angles to this first axis, each of which corresponds to the engagement of a gear or the neutral position. This control member is moved into these positions under the action of appropriate actuators: normally, a first multi-position actuator is used to control the displacements along the first axis, while a second actuator, also multi-position and moving along a second axis at right angles to this first axis, is used to control the angular displacements about this first axis.
The above-mentioned actuators are normally actuated by pneumatic, hydraulic or electrical methods and are controlled by relative actuation means; in the case of hydraulic actuation, each actuator is in particular driven by a plurality of suitably combined electrovalves.
This means that the above-mentioned control member requires, for its actuation, the use of various relatively complex hydraulic components, for instance multi-position actuators, valves, stroke regulation members and position transducers which require high-precision mechanical processing and give rise to constructional arrangements that are of high cost.
In order to remedy these drawbacks, gear change control devices are also known from Italian Patent Application TO96A001035 in the name of the applicants which make it possible to carry out both the selection of the rows of gears and the engagement or disengagement of the gears themselves using a single multi-position hydraulic actuator of conventional type.
These devices substantially comprise a control member moving axially to carry out a maneuver to select the row of gears and rotating about its axis, under the thrust of an output member of the above-mentioned multi-position actuator, to carry out a maneuver to engage or disengage the gears themselves. In particular, the control member selectively actuates, during its displacements, a plurality of gear engagement members and is mounted coaxially and in a moving manner in a cylindrical drum, which may be made selectively rigid with a fixed support unit of the gear change control device in a plurality of angular positions corresponding to respective gear selection rows.
An engagement member coupled within a cam defined by a groove obtained on the lateral wall of the drum and formed as a broken line is also fixed on the control member. This cam comprises a plurality of rectilinear axial stop sections of the control member, whose number is equal to the rows of gears, disposed at different axial heights and angularly offset from one another, and a plurality of oblique sections connecting the stop sections.
In order to move from one gear to the next within the same row, the drum is kept angularly mobile with respect to the support unit and rotates rigidly with the control member actuated by the actuation of the actuator. In order to move, however, from a gear of a particular row to a successive gear of an adjacent row, the drum is made rigid with the support unit and the actuation of the actuator therefore causes the engagement member to slide within the cam which, by means of one of its oblique sections, guides the control member, displacing it both axially and angularly.
The above-mentioned gear change control device, although it is actuated by a single hydraulic actuator, thereby simplifying the hydraulic actuation circuit, has the drawback that it needs, for correct operation, to be associated with a gear change of high precision, i.e. whose components have small dimensional tolerances and whose internal operating clearances are limited, thereby increasing the costs involved.
Since the control member has a single guide cam, the operating clearances normally present in the gear change at each maneuver to engage and disengage the gears tend to be added together causing a phase difference between the positions occupied by the engagement member along the cam and the corresponding positions of interaction between the control member and the gear engagement members, leading to imprecise actuation of these engagement members.
The object of the present invention is to provide a control device for a gear change of a vehicle, which is free from the drawbacks associated with the control devices of known type as described above.
This object is achieved by the present invention which relates to a control device for a gear change of a vehicle comprising:
a support structure,
a control member borne by the support structure such that it can move in translation along a first axis and rotate about this axis in order to carry out a maneuver to select the row of gears and a maneuver to engage or disengage the gears themselves,
actuator means cooperating with the control member which can be selectively actuated in order to displace this control member according to a predetermined movement selected from two possible movements, respectively in rotation and in translation, and dispose it, for each row of gears, in a neutral position and two engagement positions of respective gears,
cam and tappet means interposed between the support structure and the control member which can be selectively actuated in order to associate components of movement in rotation and in translation of the control member during the actuation of the actuator means, characterized in that the cam and tappet means comprise a tappet member borne by the control member or the support structure and a guide member rigid with the other of the control member and the support structure and provided with a series of cams parallel to one another and each adapted to be selectively engaged by the tappet member in order to guide the displacement of the control member between adjacent engagement positions of adjacent rows during the actuation of the actuator means.